Circuit breaker



Sept 7, 1943. l o. S. JENNINGS 2,329,053

CIRCUIT BREAKER 5 SheesnShee't l Filed June 8, 1940 Sept 7, 1943. o. s. JENNNGS 2,329,053

CIRCUIT BREAKER 5 SheetsmShem: 2

Filed June 8, 1940 JJ. ML/@1, BY

i qdfAT/ORNEY 2 Sept., '7g 1943. o. s. JENNzNGs 29329;()53

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Patented Sept. 7, 1943 CIRCUIT BREAKER Oliver S. Jennings, Pittsburgh,v Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 8, 1940, Serial No. 339,466 27 Claims. (Cl. 20o-880 The invention relates to circuit interrupters in general and more particularly to circuit breakers tor controlling lighting and moderate power circuits.

Upon closing of tungsten lamp lighting circuits, and motor circuits, the current may rise during the `irsi; half cycle to as high as approximately 1000% of the normal rated current. The iirst requirement of a circuit breaker for controlling such circuits is that it must not trip open in response to the normal initial current rise upon closing of the circuit. The circuit breaker should, however, trip substantially instantaneously, i. e., in as short a time interval as possible, upon the occurrence of overload currents in excess of 1000% oi' the rated current. Furthermore, it is desirable that the circuit breaker be operable to trip quickly, i. e., with a relatively short time delay action, in the intermediate range of overload currents, for example, from about 200% to 1000% rated current, in order to minimize the possibility of damage by overload currents in this range. A remote short circuit or a high resistance fault may occur which may produce a current within the above mentioned intermediate range, and unless the circuit is interrupted quickly, a re or other damage may result. For the lower range of overloads up. to about 200% rated current, the circuit breaker should be operable to trip with a relatively long inverse time delay action; as the currents in this range are not high enough tc damage the circult or apparatus unless they continue for some time, the length of time, of course, depending on the magnitude of the current.

Conventional prior art circuit breakers of the type embodying a current responsive bimetal trip element and an independently acting electro'- magnetic trip means do not provide an entirely satisfactory time-current operating characteristic for the reason that they introduce too long a time delay action between the occurrence of the overload and tripping or release of the breaker the breaker will not be tripped thereby in response to the initial currentvrise on closing of The electromagnetic trip means has no effect in the case of overloads below this predetermined value, and the bimetal trip velement provides an undesirably long time delay action before tripping the breaker in the intermediate range of overloads.

Although standard fuses for protecting lighting or motor circuits operate to interrupt the circuit in ashorter time interval than time delay circuit breakers, they do not possess the important advantage of being resettable and manually operable as in the case o fA a circuit breaker.

Also the usual types of fuses of a. rating corresponding to that of a given thermal circuit breaker operate too fast in the lower range of overload current, i. e., up to about 200% or 300% rated current. As a result fuses of larger rating are required in order vto provide suiiicient time delay for such light overloads.

f An object of the invention isthe provision of a circuit breaker having an improved time-current operating characteristic.

Another object of the invention is the provision of a circuit breaker embodying a thermally and magnetically responsive trip device which is operable to trip the breaker faster in response to currents within a predetermined intermediate range of overload currents, for example, in the range from about 200% to 1000% rated current,

than the usual commercial thermal magnetic cir-y cuit breakers of which I am aware.

Another object of the invention is the provision of a circuit breaker as previously described embodying an electromagnet which is operable to cause substantially instantaneous tripping of the breaker upon the occurrence of overload currents in excess of a predetermined magnitude.

yAnother object of the invention is the provision of a circuit breaker embodying an improved thermally and magnetically responsive trip device which provides an improved and more uniform time-current operating or tripping characteristic.

Another object of the invention is the provision of an improved thermally controlled circuit breaker which can be reset substantially instan- A taneously after tripping without waiting for the `thermal trip element to cool appreciably.

Another object of the invention is the provision oi a circuit breaker embodying means including a thermally responsive bimetal trip element for controlling tripping of the breaker characterized by the fact that the bimetal trip element does not do any work'or overcome any force to cause tripping of the breaker.

Another object of the invention is the provisionl of a circuit breaker embodying means including a thermally responsive bimetal trip element for controlling tripping of the breaker characterized by the fact that the movement of the bimetal element which results in tripping of the breaker is neither restrained nor limited at any time.

Another object of the invention is the provision of a circuit breaker embodying a latch which is releasable to cause opening of the breaker and a thermally responsive bimetal element for controlling the latch, the construction being characterized by the fact that the movement of the bimetal element which results in release of the latch is not restrained or limited by the latch or any other element at any time.

Another object of the invention is the provision of a circuit breaker embodying a latch, or equivalent holding means, which is movable to an unlatched or released position to cause opening of the breaker, means acting to move the latch to unlatched position, and a bimetal element yieldably opposing movement of the latch which normally restrains the latch in latching position but which is responsive to the current of the circuit to permit unlatching.

Another object of the invention is the provision of a circuit breaker embodying a latch which is movable to an unlatched position to cause opening of the breaker, electromagnetic means energized by the current of the circuit acting to move the latch to unlatched position, an adjustable spring means also acting to move the latch to the unlatched position, and a bimetal element which normally opposes unlatching `oi' the latch but which is responsive to the current to permit unlatching.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof. will be best understood from the following detailed description of several embodiments thereof when read in conjunction with the accompanying drawings, in which:

Figure 1 is an elevational view of a circuit breaker embodying the features of the invention, the breaker being shown in closed-circuit position; A

Fig. 2 is a view similar to Fig. 1 showing the circuit breaker in the manually-opened position;

Fig. 3 is a fragmentary view showing the parts of the trip device in an instantaneous position just prior to tripping of the circuit breaker;

Fig. 4 isa view showing the circuit breaker in the tripped open position;

Fig. 5 is a fragmentary view of a modiilcation of the invention;

Fig. 6 is a sectional view taken substantiallyY along the line VI-VI of Fig. 2 and looking in the direction of the arrows; and

Fig. 'l is a view showing time-current operating curves plotted on log scale illustrating the tripping or operating characteristic of a circuit breaker embodying the novel trip device of the present invention as compared to that of a circuit breaker having the same contact operating mechanism with a trip device embodying a bimetal trip element of the same size but which acts to directly move the breaker latch to released position and an independently operable electromagnetic trip means arranged to operate only when the current exceeds 1000% of the rated current, and also as compared to a standard high speed plug fuse of corresponding rating.

Referring to the drawings, the circuit breaker is mounted on abase 3 of insulating material and projecting on opposite sides of the frame.

and the opposite breaker terminal 23 is electrically connected to one terminal of the trip device Il, the other terminal of the trip device being electrically connected by a exible shunt conductor 25 to the pivoted switch arm I5 which is of conducting material. The switch arm I5 and the operating mechanism I1 are supported on a U-shaped frame 21 which is secured to the base 9 with its spaced side walls projecting perpendicular to the base. The switch arm I5 is pivoted about a fixed pivot 29 between the side walls of the frame 21 for movement to open and to closedcircuit position. Counter-clockwise or opening movement of the switch arm I5 is limited by a stop comprising a stud 3| which projects inwardly from one of the side walls of the frame 21.

'I'he operating mechmanism I1 for the switch arm comprises a pair of springs 33 which act to move the switch arm to open-circuit position, a releasable lever 35 normally restrained by a latch of the trip device I3 and which is releasable thereby on overload of the circuit to cause automatic opening of the breaker, an operating toggle consisting of a pair of toggle links 31 and 39 connecting one end of the releasable lever and the switch arm, and a manual operating lever 3| connected to the knee of the toggle by a link 43 for manually operating the breaker.

The releasable lever 35 is pivoted intermediate its ends, between the side walls of the frame 21, on ya fixed pivot pin l5 mounted at the outer end of the frame 21. The pivot pin 45 extends through aligned openings provided in the side walls of the frame 21 with its ends The opening springs 33 which are disposed on opposite sides of the frame 21 are connected at one end to the projecting ends of the pivot pin l5 and at the! other end to a transverse pin 41 secured to the switch arm I5.

The toggle links 31 and 33 are pivotally connected together by a knee pivot pin 49, and the outer end of the link 31 is pivoted to one end of the releasable lever 35 at 5I so that this lever forms a support for one end of the toggle. The other toggle link 39 is pivotally connected to the switch arm I5 at 53, and this link is provided with a shoulder 55 which cooperates with a projection 51on the other toggle link 31 to prevent movement of the toggle beyond the overset position shown in Fig. 1.

The releasable lever 35 is biased in a counterclockwise direction by a component of the force oi' the opening springs 33 transmitted thereto through the operating toggle 31-39. The lever 35, however, is normally latched in an operative position and prevented from moving counter-clockwise by a latch element of the trip device I9, thus normally providing an operative support for the outer end of the operating toggle. i

The manual operating lever 4I is pivoted intermediate its ends between the side walls of the frame 21 on the pivot pin 45, and the inner end of this lever is connected to one end of i operative position. in Figs. 1-4, the latching surfaces of thelatch the link 43 through a pin and slot connection 59. The other end of the link 43 is pivotally connected to the knee pivot pin 49 of the operating toggle. y A

Movement of the manualoperating lever 4| to the closed position moves the operating tog- 81e 3,1-39 to the overset position and thereby 'causes movement of the` switch arm I5 to the closed-circuit position, as shown in Fig. l. The switch arm I5 is held in closed position by the overset toggle and the lever 35 which is latched in operative position by the trip device. To manually open the circuit breaker the manual operating lever 4I is moved in a clockwise direction to open position. This movement of the operating lever is transmitted to the toggle 31-39 by the link 43 causing the toggle to collapse and the switch arm to be moved to opencircuit position b'y the springs 33. The manually open position of the breaker is shown in Fig. 2.

The trip device I9 is operable in response to predetermined overload conditions to cause automatic opening of the circuit breaker by releasing the lever 35. When the lever 35 is released the springs 33 move the switch arm I5, the toggle 31-39 and the lever 35 to the open position shown in Fig. 4. This automatic opening operation of the breaker takes place irrespective of the position of the. manual operating lever 4I, i. e., the contacts are entirely trip free of the manual operating lever. y

Before the breaker can be reclosed following a tripping operation, it is ,necessary to reset the releasable lever 35 to latched position. This is accomplished by manually moving the operating lever 4I to open position. 'I'his movement of the operating lever 4I is transmitted to the releasable lever 35 through thel link 43 and the operating toggle 31-39 causing clockwise movement of the lever 35 to the latched position where it is relatched by the latch element of the trip device I9. After the releasable' lever 35 has been reset, the breaker may be closed by moving the operating lever 4I to the closed position.

The trip device I9 is mounted on a frame or bracket 6I secured to the base 9 and comprises, in general, apivoted latch lever 63 controlled by an electromagnet 65 and a thermally responsive bimetal element 61. The electromagnet 65 comprises a U shaped core 69 of magnetic material which is secured to the outer end of the frame 6I, a; movable armature 1I also of magnetic\ material carried by the latch lever 63, and an energizing winding 13 wound upon one leg of the core 69. o

The latch lever 63 is preferably formed of a single piece of metal, and has a yoke shaped portion providing spaced legs which straddle and are pivoted to the longer leg of the magnet core 69' by means of a pivot pin 15. The latch lever is provided with an extension 11 having a latch element or projection 19 struck out therefrom which is adapted to engage a latch surface 8| or notchon the free end ofthe releasable lever 35 to hold the releasable lever in In the embodiment shown projection 19 and the lever 35 when in latching engagement -are perpendicular to a line projected from the center of the pivot axis so that the breaker springs 33 do not bias the latch lever 63 in either direction.

A tension spring 83 is anchored at one end to a projection 85 of the latch lever 63. The coils of the other end of the 'spring 83 engage the threads of an adjusting screw 81 which extends through an opening provided in the back of the 1 magnet core 69. The spring 83 is thus connected c to the adjusting screw and its strength is adjustable thereby. The spring 83-acts to bias the latch comprises a at strip of bimetallic material bent in U shape and secured at one end to a bracket 89. The bracket 89 is, in turn, secured to the lever 63 to' the unlatched or released position, and the strength of the spring is preferably more than suillcient to overcome the latch load and release the lever` A35.

The thermally responsive bimetal element 61 end of the latch lever 63 and is insulated there-- from by an insulating button secured to the free end of the latch lever 63.

'I'he bimetal element 61 normally assumes the position shown in Figs. l and 2 and opposes movement of the latch lever 63 to the unlatched position so as to normally restrain the latch lever in latching position. When the bimetal element 61 is heated a predetermined amount, its free end flexes or is moved in a direction away from the breaker mechanism I1 to permit movement of the latch lever 63 toward the unlatched position. Y

The energizing winding 13 of the electromagnet 65, and the bimetal element 61 are electrically connected in series with the contacts II and I3 of the circuit breaker so as to be traversed by the current flowing in the circuit controlled by the breaker. y

The electromagnet 65 when energized exerts a force on the latch lever 63 acting to move the lever to the unlatched position, the force varying with the magnitude of the current of the circuit. The design of the electromagnet is preferably such that it will exert sufficient pull or force on the latch lever 63 for overload currents in excess of a predetermined magnitude, for example about 1000%y of the rated current to move the latch lever 63 to the released position against the opposing force of the bimetal element 61 irrespective of how much the bimetal element is heated. At normal current values the combinedforce of the electromagnet 65 and. that of the biasing spring 83 is insuficient to overcome the opposing force of the bimetal element 61 so that the latch lever 63 remains in latching position as long as normal current conditions persist.

creases its restraining force which opposes release of the latch lever 63. At the same' time the pull or unlatching force of the electromagnet 65 increases as the currentk is increased. The latch lever 63 is moved to the unlatched position as soon as the combined force of the electromagnet w 65 and spring 83 is suillcient to overcome the relectromagnetic trip meansv tained principally by reason of the fact that the opposing i'crce c; ine :imetal eis-nient 6l and the latch load of the vcreaker. The bimetal element 61 introduces a time delay action between the occurrence of the overload and tripping or release of the circuit breaker mechanism up to a predetermined current value, for example, up to about 1000% of the rated current. Upon the occurrrence of overload currents in excess of this predetermined magnitude the electromagnet 65 exerts sufficient pull to effect substantially instantaneous tripping of the breaker irrespective of the opposing force of the bimetal element 61, i. e., even though the bimetal element may not have been heated a substantial amount. The time delay action introduced by the bimetal element 61 in the range of overloads below the predetermined instantaneous tripping value varies inversely with the magnitude of the current, the time delay being greatest for light overloads and decreasing as the value of the current increases.

The novel construction and arrangement of parts of the trip device, however, are such that the device operates to trip or release the circuit breaker mechanism faster, i. e., with considerably shorter time delay action in the intermediate range of overload currents, for example, in the range from about 200% to 1000% rated current than conventional circuit breakers having a bimetal trip element and an independently acting This result is obelectromagnet 65 exerts an unlatching force at all times when it is energized, which force varies with the magnitude of the current, while the bimetal element resilientiy opposes unlatching with a force which decreases as the element is heated by the current. 'I'he electromagnet 65 is energized a sufficient amount when the current reaches the beginning of the intermediate range to exert considerable unlatching force and this force increases as the current increases. As a result less heating of the bimetal element is required to cause unlatching than if the force of the electromagnet were not presentin this range. Thus the electromagnet has the effect of decreasing the time factor or thermal characterist.' introduced by the bimetal element. The spring 83 exerts a substantially constant unlatching force which is supplemented by the variable force of the electromagnet. The spring 83 also has the effect of altering the time delay action due to the fact that it adds a constant to the force of the electromagnet, thus decreasing the rate at which the combined force of the electromagnet and spring increases. This effect of the spring however decreases rapidly as the current increases the pull of the electromagnet.` The force exerted by the electromagnet 65 for light overloads is relatively small and hence does not have any substantial effect on the time delay action of the bimetal element for such overloads.

Upon the occurrence of overload currents in excess of a predetermined magnitude, for example, about 1000% rated current, the electromagnet 65 exerts sumcient pull or unlatching force to trip or release the circuit breaker mechanism substantially instantaneously irrespective of the opposing force of the bimetal element 61.

Fig. 7 illustrates the improved operating chariacteristic obtained by a circuit breaker embodying the novel trip device of the present invention as compared to that obtained by a breaker having the same contact operating mechanism but using a conventional thermal-magnetic trip device in which the same size bimetal element acts to directly release the latch and in which the electromagnetic trip means acts independently of the bimetal element and is arranged to operate only when the current exceeds 1000% rated load, and also as c/mpared to a standard plug fuse. Referring to Fig. '7, curve A illustrates the operating characteristic obtained by a breaker embodying the novel trip device of the present invention. Curve B shows the operating characteristic obtained with the same contact operating mechanism but using a conventional thermalmagnetic trip device with independently acting electromagnetic trip means as described above. Curve C shows the operating characteristic of a standard plug fuse of corresponding rating.

The dotted line B which is added to curve B represents a continuation of the operating characteristic provided by the bimetal trip element which would be present if the independently acting electromagnetic trip means were omitted.

It will be noted from the curves that the novel trip device of the present invention provides a faster tripping action, i. e., shorter time delay action for theintermediate range of overload currents than obtained by the conventional thermalmagnetic trip indicated by curve B.

The curve of the fuse illustrates that it operates too fast for the lower range of overload currents. 'I'his is an undesirable feature as it results in unnecessary interruptions of service. Light overloads can continue for a considerably greater time than the fuse will permit without damaging the circuit. To overcome this disadvantage, fuses of greater actual rating than the rating o f the circuit are generally used.

A modied construction of the trip device is illustrated in Fig. 5. The same reference characters have been used in connection with this figure to designate the elements which correspond to those of the original embodiment. In this modification oi the invention, the point of engagement of the latching surfaces is oflset relative to the pivot axis of the latching lever 33, and the line of engagement of the latch surfaces is disposedat an angle with respect to a line drawn 'thereto from the pivot axis 15, so that the opening spring 33 of the breaker assists and supplements a spring 83' to bias the latching lever to the unlatched position. The adjusting spring 83 may be omitted entirely if desired and the latching lever 63 biased to the unlatched position by a component of the force of the main spring 33 oi.' the breaker in the manner described, that is by offsetting the latch engaging surfaces with respect to the pivot axis oi' the latching lever and/ or having the line of engagement of the latch surfaces disposed at the desired angle with respect to a line drawn from the pivot axis 15 to the center point of engagement of the latch surfaces. In Flg. 5 the free end of the latching lever 3l is made shorter and the latch element 19' longer so that the point of engagement of the latch surfaces is oil'set relative to the pivot axis 1l. The line of engagement of the latch surfaces of the element 1l and that of the lever 35 are disposed at an angle to a line projected from the center of the pivot axis 15 to the midpoint of the engaging latch surfaces. Thus the breaker opening spring acts to move the latch lever to unlatched position.

One important advantage of the present invention is the fact that the bimetal element is moved free of any restraint at all times, and is not required to do any Work in controlling tripping of the circuit breaker. Another important advan- 2,329,053 tage 4ai' the invention is the fact that the concombined force of the spring 88 and the electromagnet 85 deilects the bimetal element 81 just a sumcient amount to cause unlatching. The instant the current is ruptured, the force of the electromagnet 65 disappears and the-bimetal element 81 starts to cool. With the absence of the force of the magnet the bimetal element 81 is deflected less than at the time of unlatching. Consequently, the free end of the bimetal element immediately returns a small amount due to its resiliency, thereby causing the latch to assume a latching position, and the breaker can be manually resetat once without waiting for the bimetal element to cool a substantial amount. This is a very unusual feature for a thermal circuit breaker and one which is particularly desired by the trade as it reduces delays ordinarily present with the usual thermal circuit breakers.

' Evenwith very heavy short circuit currents, the

delay in resetting maybe reduced from 200 or 300 seconds required by prior art devices to or seconds or less.

The adjusting screw 81 provides a means for adjusting the strength of theispring 88 to vary the operating characteristic of the trip device.

It will be noted that the novel construction of the' trip device and the adjusting means provides for varying the operating characteristic by altering the set or position of the bimetal element at its free or Working end to change the calibration. Previous designs utilize constructions which vary the calibration by altering the position of the bimetal element at .its xed end, or by altering the position of the latch relative to the bimetal element. i

Although a particular construction of contact operating mechanism I1v has been shown and described, it is obvious that various other types and constructions of contact operating mechanisms may be used with the novel trip device of the present invention.

It will be readily understood by those skilled in the art that the operating characteristic of the trip device may be varied by changing the design of the electromagnet 65 and also bychanging the strength of the spring 83 or releasing blason the latch and/or by changing the design of the bimetal element. The limits of the so-called intermediate range of overloads given (about 200% to 1000% rated current) are to be con.-

sidered merely by Way Vof example and thesevmay be varied considerably in the manner described above to suit particular requirements.

While the invention has been disclosed in ac-` cordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details and arrangement of parts may be made without departing from some of the essential features of the invention. `It is desired, therefore, that the appended claims shall be accorded the broadest reasonable construction consistent with the language and the prior art.

portion movable in one direction when said element is heated a predetermined amount to cause said contacts to be opened by saidl means, elec.- tromagnetic means for applying a force to said element which varies with the magnitude of the current of the circuit tending to move said portion of the element in said one direction, and spring means applying an additional force to saidelement tending to move said portion in said one direction.

2. A circuit breaker comprising relatively movable-contacts, actuating means for opening and closing said contacts, a current responsive bimetal element heated in response to the current flow in the circuit, said element having a portion movable in one direction when said element is Y heated a predetermined amount to allow said actuating means to automatically open said contacts, electromagnetic means energized by the current of the circuit applying a force to said portion of said element tending to move said portion in said one direction, and spring means also applying a force to said portion of the bimetal element tending to move it in said one direction.

3. A circuit breaker comprising relatively mov able contacts, a member releasable to cause openlng of said contacts, a pivoted latch for normally restraining said member, means including a spring applying a force to said latch to move said latch to released position, means for adjusting said spring to vary the force applied thereby to said latch, and a bimetal element heated in response to the current of the circuit having a portion which yieldably opposes release of said latch and which is moved to permit release of said latch when said element is heated a predetermined amount.

4. A circuit breaker comprising relatively movable contacts, a member releasable to cause opening of said contactsa movable trip member operable to cause release of said member, an electromagnet energized by current of the circuit and a spring both applying a force to said trip member to cause a tripping operation thereof, and a bimetal elementfheated in response to the current of the circuit, said bimetal element having a portion which opposes tripping movement of the trip member and normally maintains said trip member in normal position and which is moved when said element is heated a predetermined amount to permit tripping movement of said trip member.

5. A circuit breaker comprising relatively movable contacts, operating means therefor including a` spring biased member releasablev to cause automatic Aopening of said contacts, a movable latch for normally engaging and restraining said member, spring means applying a force to said latch acting to move said latch to released position, an electromagnet energized in response to the current of the circuit applying a force acting to move said latch to released position, a bimetal element free of connection with said latch heated in response to the current of the circuit, said element having a portion which normally opposes release of said latch and which is moved under the influence of said force applying means free of any restraint by said latch when said element is heated a predetermined amount to permit release vof said latch.

a movable latch for normally restraining said member, means including a spring and an electromagnet energized by the current of the circuit both applying a force to said latch suillcient to move said latch to released position, a bimetal element free of connection with said latch heated in response to the current of the circuit, said element having a portion which engages and yieldably opposes release of said latch and normally restrains said latch in latching position and which is moved under the influence of the force applying means free of restraint by said latch when said element is heated a predetermined amount to permit release of said latch.

7. A circuit breaker comprising relatively movable contacts, operating means therefor, a trip member movable from a normal position to a tripping position to cause automatic opening of said contacts, means operable to cause tripping movement of said member comprising a bimetal element heated in response to the current of the circuit having a portion which is moved when said element is heated a predetermined amount to allow tripping movement of said member, electromagnetic means energized in response to the current of the circuit for applying a force to said portion of said element tending to move said portion to cause tripping movement of the trip member, and means independent of said electromagnetic means for applying a predetermined additional force to said portion of said bimetal element tending to move it in a direction to cause tripping movement of said trip member.

8. A circuit breaker comprising relatively movable contacts, operating means therefor including a member releasable to cause automatic opening of said contacts, means operable to cause release of said member comprising a bimetal element heated in response to the current of the circuit having a portion which is moved when said element is heated a predetermined amount to permit release of said member, electromagnetic means energized in response to the current of the circuit for applying a force to said portion of said element tending to move said portion in a releasing direction, and means independent of said electromagnetic means for applying a predetermined additional force to said portion of said element tending to move it in the releasing direction, said electromagneticmeans being operable to effect instantaneous release of said member upon the occurrence of overloads in excess of a predetermined magnitude.

9. A circuit breaker comprising relatively movy able contacts, operating means therefor including an element movable to a tripping position to cause automatic opening of said contacts, anv

10. A circuit breaker comprising relatively movableontacts, operating means therefor including a member releasable to cause automatic opening of said contacts, a movable latch for normally restraining said member, electromagnetic means energized by the current of the circuit acting to move said latch to released position, means in addition to said electromagnetic means also acting to move said latch to released position, and a bimetal element heated in response to the current of the circuit having a portion which yieldably opposes release of said latch and which is moved free of any restraint when said element is heated a predetermined amount to permit release of said latch.

11. A circuit breaker comprising relatively movable contacts, operating means therefor, s trip member movable from a normal position to a tripping position to cause opening of said contacts, electromagnetic means energized by the current of the circuit acting to cause movement of said trip member to tripping position, additional means also acting to move said trip member to tripping position, and a bimetal element heated in response to the current of the circuit having a portion which yieldably opposes tripping movement ci said trip member and normally maintains said trip member in normal position and which yields when said element is heated a predetermined amount to "permit tripping movement of said trip member.

12. A circuit breaker comprising relatively movable contacts, operating means therefor including a member releasable to cause automatic opening of said contacts, an electromagnet energized by the current of the circuit having a pivoted armature carrying a latch for normally restraining said member when said amature is in an unattracted position, said latch effecting release of said member when said armature is moved to attracted position, means biasing said armature toward attracted position with a predetermined force, and a bimetal element heated in response to the current of the circuit having a movable portion which yieldably opposes movement of said armature to attracted position and which is moved when said element is heated a predetermined amount to allow release of said member, said electromagnet being operable to substantially instantaneously effect release of said member upon the occurrence of overloads in excess of a predetermined magnitude.

i3. A circuit breaker comprising relatively movable contacts; operating means therefor including a member releasable to cause automatic opening oi' said contacts, an electromagnet energized-by the current of the circuit having s. pivoted armature carrying a latch for normally restraining said member when said armature is in an unattracted position, said latch effecting release of said member when said amature is moved to attracted position, adjustable spring means biasing said armature toattracted position, and a bimetal element heated in response to the current of the circuit having a portion which normally opposes movement of said armature ltoward attracted position and which is moved free of any restraint when said element is heated a predetermined amount to permit release of said latch.

14. A circuit breaker comprising relatively movable contacts, operating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, means biasing said trip member to tripping position with a predetermined force, electromagnetic means energized by the current of the vmovable contacts, operatingmeans therefor including a handle for manually operating said contacts and a spring biased member releasable to cause automatic opening of said contacts, said member being resettable after release by movement of said handle, a movable latch for' normally restraining said releasable member, means comprising an electromagnet energized by the current of the circuit acting to move said latch to released position, a thermally responsive bimetal element having a portion which yieldably opposes release oi said latch and normally restrains said latch in latching position, said portion being disposed to deflect free of any restraint t all times in response to heating of said element, said element being heated in response to the current of the circuit and decreasing its restraining force as its temperature is irl-Z creased, said portionl of said element being moved to permit release of said latch when said element is heated a predetermined amount and being operable to return said latch to a latching position immediately following interruption of the circuit and before said. element has cooled a substantial amount.

16. A circuit breaker comprising relatively movable contacts, operating means therefor including a spring biased member releasable to cause opening of said contacts, said member being resettable manually after release thereof, a movable latch for normally engaging and vrestraining said member, means comprising an electromagnet energized by the current of the circuit acting to cause movement of said latch to released position, a thermally responsive bimetal element having a portion which ry-leldably opposes release o'f said latch by said means comprising said electromagnet, said bimetal element being heated in response to the current of the circuit and acting to decrease its restraining force which opposes release of said latch as the temperature of said element is increased, said portion of the bimetal element being moved free of any restraint when said element is heated a predetermined amount to permit release of the latch, and said portion of the element moving a sufficient amount in lthe opposite direction immediately upon deenergizationY of said electromagnet following interruption of the circuit and before said elementl has cooled a' substantial amount to cause return of said latch to latchin'g position due to the fact that said portion is deflected less upon removal of the force of the electromagnet that at the time of unlatching.

17. A circuit breaker comprising relatively movable contacts, operating means therefor including a spring biased member releasable to cause opening of said contacts, a movable latch for normally restraining said member, said latch being biased to unlatched' position by a component of the force acting to move said member, electromagnetic means energized by vthe current of the circuit acting to move said latch to unlatched position, a thermally responsive bimetal element which yieldably opposes release of said latch and normally restrains said latch in latchlng position, said element being heated in to decrease the restraining force which opposes release of said latch as the temperature of said element ls increased, said element being defiected free of any restraint when heated and permitting release of said latch when heated Aa predetermined amount. f

18. A circuit breaker comprising relatively movable contacts, operating means therefor including a handle for eifecting'manual opening and closing of said contacts and a member releasable to cause opening of said contacts irrespective of the position of said handle, a movable latch for normally restraining said member, means comprising an electromagnet energized by the current of the circuit acting to cause movement of said latchto released position, ad-

ditional means also acting to move said latch to released position, a. bimetal element heated in response to the current of the circuit and mounted to deflect free of any restraint at all times in the direction in which it defiects when heated, said element acting to restrain release of said latch by said means" comprising said electromagnet and said additional means, the restraining force provided by said element against release of the latch decreasing as the temperature of said element increases.1`

19. A vcircuit breaker comprising relatively movable contacts, operating means therefor, a trip member movable from a normal position to a tripping position to cause opening of said contacts, spring means applying` a force acting to cause movement of said trip member to tripped position, a thermally responsive bimetal element having a portion which opposes tripping movement of said trip member by said spring means and normally providing a restraining force which prevents tripping movement of said trip member by said spring' means, said portion of said element gradually decreasing the restraining force as the temperature of said element increases, and electromagnetic means energized by the current 'of the circuit applying a force to said trip member.

20. A circuit breaker comprising relatively movable contacts, actuating means therefor including a trip device operable to cause opening of said contacts, said trip device comprising electromagnetic means and an independently mounted thermal element both energized in response to the current of the circuit and normally opposing each other, said electromagnetic means exerting a force acting to trip the breaker which increases as the current increases, while the opposing force of the bimetal element gradually decreases as it is heated by the current, and spring means exerting an additional force acting to trip the breaker.

21. A circuit breaker comprising relatively movable contacts, a. trip device operable to cause opening of said contacts comprising two springs which normally oppose each other, one of said f springs exerting a force acting to trip the breaker and the other of said springs being of bimetallic material and heated in response to the current of the circuit to regulate the action of the first mentioned. spring, and electromagnetic means -for producing an additional force acting to trip the breaker.

22. A circuit breaker comprising relatively movable contacts, a trip device operable to cause opening of said contacts including a thermally responsive bimetal element having a free working end which is moved to cause said breaker to response to the current oi' the circuit and acting be tripped by said trip device when said element lis heated a predetermined amount, and adjusting means manually operable to alter the set of the bimetal 'element at its working end to vary the time-current operating characteristic of said element.

23. A circuit breaker comprising relatively f movable contacts, a trip device operable to cause opening of said contacts including a thermally responsive bimetal element having a free working end which-is movable free of any restraint to cause said breaker to be tripped by said trip device, and means for altering the set of the bimetal element at its working end to vary the time-current operating characteristic oi' said element.

24. A circuit breaker comprising relatively movable contacts, operating means therefor including a trip member movable to a tripping position to cause automatic opening of said contacts,

spring means biasing said trip member toward tripping position, a bimetal element heated in response to the current of the circuit which normally opposes tripping movement of said trip member and which is moved free of any restraint when said element is heated to allow movement of said trip member toward tripping position, and current responsive means acting to move said trip member to tripping position.

25. A circuit breaker comprising relatively movable contacts, operating means therefor including a member releasable to cause automatic opening of said contacts, a movable trip member operable to cause release of said member, an electromagnet energized in response -to the current of the circuit acting to cause tripping operation of said trip member, spring means biasing said trip member to tripping position, and a bimetal element having a portion which opposes tripping movement of said trip member and normaily maintains said trip member in normal position and winch is moved when said element is heated a predetermined amount to allow trip ping movement of said trip member.

26. A circuit breaker comprising relatively movable contacts, operating means for opening and closing said contacts including a handle for manually operating said contacts and a member movable to cause automatic opening oi said contacts irrespective of the position of said handle, means comprising a spring and electromagnetic means energized in response to the current oi the circuit for applying a. force to move said member, and a current responsive bimetal element heated in response to the current of the ycircuit and having a free portion disposed with its nat side in the path of movement of said member to normally oppose said movement, oi said member, said bimetal element at times deiiecting free oi any restraint when heated and allowing said member to be moved by said means to effect opening of said contacts when said bimetal element is heated a predetermined amount.

27. A circuit breaker comprising relatively movable contacts, operating mechanism therefor including an operating handle operable to close said contacts, a member releasable to cause i opening of said contacts irrespective of the 

